On Apr. 7, 1989, the applicant submitted to the Chinese Patent Office a patient application under the title "A new Type of Screw-driven Mechanism", the number of this patent application is 89102066.7 now Chinese patent No. 1,046,213. In FIG. 11 of said application is disclosed a screw stem with the journals at its two ends rotatably supported in bearings disposed in fixed bearing supports, and under the action of an eccentric cam sleeve and a uni-directional pawl, a half-nut can be made to slide up and down along a guide post, whereby the meshing and disengagement of the screw and the half-nut can be effected. This prior art is simple and useful, however, it can only be applied to relatively rigid screw stems of a relatively short length, otherwise the screw stem will likely be bent and will not work properly.
The object of the present invention is to overcome the shortcomings of said prior art and to provide a synchro-clutching mechanism suitable for application on screw stems of various lengths.